Abstract:Diffusion coefficient of chloride ion in four type textural soils at various water contentunder different temperature were measured by the diffusion-cell method using36Cl labelledNaCl solution, The results showed that the diffusion coefficient(D)in the soil increased butthe activation energy decreased with increasing soil water content, which indicated that theforce to be overcome during the diffusion was lower at higher soil water content. The D valuedecreased with increasing soil water tension(S).The relation could be descilbed by the pow-er equation in the form of D=sS-b, The D value increased with increasing temperature, andincreasing temperature 10℃ from 5℃ to 45℃ caused the D value increased by 10%~30%with average of nearly 20%. The relationship between D value and soil water content as wellas temperature could be described by the nonlinear regression equation. Moreover,it wasfound that the D value increased with increasing clay content of soil under same water ten-sion,in general,the correlation between D and clay content was significantly positlve.